Vapor generating and superheating unit having multiple entry of returned heating gases



May 5, 1959 P. H. KOCH 2,

VAPOR GENERATING AND SUPERHEATING UNIT HAVING MULTIPLE ENTRY OF RETURNEDHEATING GASES Filed March 2'7, 1952 4 Sheets-Sheet 1 IN V EN TOR.

7 FIG-1 BY Jazz/fife]:

ATTORNEY P. H. KOCH May 5, 1959 2,884,909 VAPOR GENERATING ANDSUPERHEATING UNIT HAVING MULTIPLE ENTRY OF RETURNED HEATING GASES 4SheetsSheec 2 Filed March 2'7. 1952 www I In I I INVENTOR, azzi L hATTORNEY y 5, 1959 P. H KOCH 2,884,909

VAPOR GENERATING AND SUPERHEATING UNIT HAVING MULTIPLE ENTRY OF RETURNEDHEATING GASES Filed March 27, 1952 4 Sheets-Sheet 3 FIGS IN VEN TOR.

F l s. 5

ATTORNEY y 5, 1959 P. H. KOCH 2,884,909

VAPOR GENERATING AND SUPERHEATING UNIT HAVING MULTIPLE ENTRY OF RETURNEDHEATING GASES Filed March 27, 1952 4 Sheets-Sheet 4 INVENTOR.

BY 6 z ATTORNEY United States Patent VAPOR GENERATING SUPERHEAT- INGUNIT HAVING MULTIPLE ENTRY OF RETURNED HEATING GASES Paul H. Koch,Bernardsville, N.J., assignor to The Babcock & Wilcox Company, New York,N.Y., a corporation of New Jersey Application March 27, 1952, Serial No.278,872 13 Claims. (Cl. 122-478) This invention relates to improvementsin combined vapor generating and superheating units.

The invention is more particularly concerned with the vapor generatingand superheating units which are utilized to supply high pressure andhighly superheated vapor to prime movers, in central power stations andmethods of operating such units. The overall efiiciency of suchinstallations is, of course, of paramount importance, and it isrecognized that the employment of high pressure vapor at the highestoptimum temperature promotes such efliciency. When it is desired tomaintain high superheat it is necessary to dispose the tubular elementsof the superheater at a position at which the heating gas is of highheat content and temperature. This is particularly true when apredetermined superheat is to be maintained over a wide load rangeincluding very low loads. A problem in the attainment of the optimumhigh superheat arises in connection with the burning of slag formingfuel. When the pertinent superheater elements are disposed in a hightemperature zone to attain the optimum high superheat, the superheaterelements accumulate slag coatings which reduce the heat absorption ratesof the superheater elements. Hence, the slagging of the superheatedtubes must be controlled from the standpoint of attaining optimum highsuperheat.

This invention involves heating gas recirculation which is utilized forgas tempering for slag control under some conditions.

.In a more specific sense, the invention involves fuel burning meansexemplified by a cyclone furnace construction burning a slag formingfuel at temperatures above the slag fusion temperature, and thedisposition of at least parts of superheater platens in the path of thecombustion products and at such a position that the pertinentsuperheater parts are, at times, contacted by slag particles in suchcondition with respect to fusion that these particles accumulate uponthe pertinent superheater parts. In a preferred embodiment of theinvention the superheater elements are arranged as pendent sup'erheaterplatens disposed within a vertically elongated secondary funnace chamberreceiving the combustion products from a cyclone furnace arrangementburning crushed coal at temperatures above the ash or slag fusiontemperatures of the coal. Parts of the dependent superheater platens aredisposed in a part of the secondary furnace chamber receiving combustionproducts including high temperature heating gases with particles offused slag suspended therein. In this arrangement; there is arecirculated furnace gas system including fan and ductw'orlc' having itsinlet downstream gas-flowwise with respect to the superheat'er andhaving its tempering gas outlet ingas" mixing cornmunication with thesecondary furnace chamber at a position upstream of the superheater.

This recirculated gas system also has a recirculated gas outletincommunication with the primary furnace chamber of' the cyclonefurnacearrangement and associated with gas flow controls to the end thatthe'flow of recirculated gas to the primary furnace chamber may be in-2,884,909 Patented May 5, 1959 creased as the load decreases. In thismanner, the optimum high superheat is maintained by decreasing the ratioof furnace absorbed heat to the total heat absorbed in superheating thevapor. Such action includes an increase in the proportion of the heat ofthe fuel in the gases carried to the superheater.

Due to concurrent increase in heat content of the gases entering thesuperheater, and due to the increase in gas mass flow over theconvection superheater, the overall Vapor heating is increased.

To control slagging conditions over the superhcater, the invention alsoinvolves means for returning the heating gases from a point downstreamgas-flowwise of the superheater and causing the entry of those gases astempering gases into the secondary furnace chamber at a positionupstream of the superheater. The invention involves variation of therate of flow of such tempering gases in accordance with changingslagging conditions involved 'in changing load or changing fuel, as wellas changing superheat and reheat requirements.

In a vapor generating and superheating unit of the pertinent type, wherethe superheating is accomplished by the combination of a predominantlyradiant superheater and a predominantly convection superheater, andwhere the reheater is a predominantly convection heater adjacent theconvection superheater, the use of returned furnace gases as temperinggases to effect a lowering of the gas temperature to the radiantsuperheater while maintaining the heat content, is effective in reducingthe otherwise inherent divergence of reheater and superheatertemperatures, with reducing load. This is particularly true where theconvection re'heater and the superheate'r section are arranged in seriesas to gas flow at a position downstream of the radiant superheater.

The type of unit involved in the invention is one in which substantiallyall of the vapor is generated in tubes defining or constituting parts ofthe walls and other boundaries of the furnace chambers and the cyclonesburning the slag forming fuel. Advantageously, the heating gases arereturned from a position downstream gasfiowwise of the superheater to azone adjacent the top of the primary furnace chamber and also adjacent apos tion through a wall of the secondary furnace chamber ahead of orbelow the superheater platens. In this zone the outlet of the system forreturning furnace gases may be considered as having a tempering gaschamber adapted to be placed in communication with the secondaryfurnace, and a recirculating gas chamber adapted to be placed incontrolled communication with the upper part of the primary furnacechamber. Gas flow control devices are associated therewith to controland vary the flow of returned heating gases to either one orboth ofthese chambers. In addition, the communication between the tempering gaschamber and the secondary furnace chamber takes place through aplurality of openings distributed along the wall of the furnace gaschamber, and in these openings there are disposed multiple louver gasflow control devices which are independently adjustable and thereforeadapted to direct the incoming tempering gases transversely of gas flowin the secondary furnace chamber and at different angles in order thatadequate mixing of the tempering gases with the other gases may beattained.

The invention also contemplates the use of an automatic control systemfor maintaining a predetermined superheatover a wide load range. Itcontemplates the control or variation of tempering gas flow fromindications related to furnace gas temperature or from load, subject topossible modification by control elements resp'onsive to final vaportemperatures and/or responsive to intermediate vapor temperature at theattemperat'or,

disposed between a predominately convectional primary superheater andthe predominately radiant secondary superheater.

The invention also contemplates control of vapor generation over a wideload range, in accordance with vapor demand and the variation andcontrol of the flow of recirculating gas to the primary furnace chamberfrom representations of steam flow-airflow, vapor temperatures, and thecharacteristics of the devices for directly controlling the recirculatedgas flow. The automatic control system contemplated by the invention isof the nature of that disclosed in the pending patent application of W.H. Rowand, Serial No. 250,268, filed October 8, 1951, now Patent No.2,840,054 issued June 24, 1958, for Power Generating and SuperheatingMethod and Apparatus Therefor.

The invention contemplates the described units and their methods ofcontrol which may render it advantageous to continue (in regulateddegrees) the introduction and mixing of tempering gas over a major partof the entire load range. Such wide range use of tempering gas flow hasbeen found to be advantageous in increasing the availability of the unitby reason of beneficial effect upon slagging conditions. One suchbeneficial effect resides in what may be termed the cumulative effect ofthe tempering gas flow upon slag accumulations resulting from thecontinuance of such flow even after and beyond the periods during whichthe gas temperatures in front of the superheater are such as would notmaintain slag particles in such condition that they would accumulate.

Such continued flow might be said to have a cumulative mechanical effectin dislodging slag accumulations which had previously been deposited.

Advantageous regulation of vapor heating may be effected by thesimultaneous entry and control of recirculating gas flow and temperinggas flow, the former introduced at a position within a water-cooledfurnace, remote from the super-heater and the latter introduced at aposition ahead of the superheater and intermediate the position ofrecirculating gas introduction and the superheater.

The invention also contemplates the coordination of tempering gas flowand recirculating gas flow to maintain optimum high superheat and reheatover wide load range in a unit which involves a predominantly radiantsecondary superheater and a predominantly convection heated reheaterdisposed in a convection gas pass beyond a secondary furnace chamber inwhich the secondary superheater is disposed. Such unit may involve thedisposition of the reheater in one or more of two parallel sub-divisionsof the convection gas pass, the remaining sub-division or sub-divisionsof that gas pass including a convection primary superheater. Becausereheat, in an installation of this type, tends to fall at a greater ratethan superheat, the gas flows in the parallel subdivisions of theconvection gas pass are dampered so as to substantially maintain optimumreheat at low loads by increasing gas flow over the reheater at theexpense of gas flow over the primary superheater. This substantiallyeliminates any necessity for reheat attemperation. However, such controlof reheat involves an increase in draft loss which can be reduced orminimized by the use of the present invention. The inventionaccomplishes such control by its effectiveness in the distribution ofsuperheater and reheater heat absorption.

This is particularly accomplished by reason of the marked effect of thevariation of tempering gas flow upon the secondary superheater which ispredominantly of radiant heat absorption. When the gas temperaturewithin the effective range of the radiant superheater is varied thattemperature efiect has an increased effect upon the thermal action ofthe secondary superheater by reason of the fourth power characteristicof its radiant heat absorption. For example, when the tempering gas flowis increased, the temperature of the gas eifective upon the Theinvention also contemplates a unit of the pertinent.

type in which optimum reheat and superheat control may be effected, inpart, by selective multiple level fuel burner control. As an example ofthe components of the unit promoting this control, the fuel burningdevices include rows of cyclone fuel burners at different levels anddischarging high temperature combustion products into a primary furnacechamber and toward a wall of vapor generating tubes common to theprimary furnace chamber and the secondary furnace chamber. In thisaspect of the invention, the flow of recirculated furnace gases in theprimary furnace chamber and along the surface of that common wall,combines with the multiple level row of burners in a cumulative effectupon the ratio of furnace absorbed heat to the heat absorbed inreheating and superheating. For example, when only the burners of thelower row are employed and with a substantial flow of recirculated gasalong the common wall, the effect is such as to produce a markeddecrease in furnace absorbed heat, and a marked decrease in the ratio offurnace absorbed heat to the heat absorbed by reheating andsuperheating.

The terms recirculated gas or recirculating gas, or similar terms, andthe term tempering gas or tempering gas flow refer, respectively, toreturned gas flow to the primary furnace chamber and returned gas flowto the secondary furnace chamber.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this specification, but, for a better understanding of theinvention, its operating advantages and the specific objects attained byits use reference should be had to the accompanying drawings anddescriptive matter which disclose several embodiments of the invention.

In the drawings:

Fig. 1 is a side sectional view, or vertical section of a vaporgenerating and superheating unit constituting a preferred embodiment ofthe invention;

Fig. 2 is a diagrammatic view in the nature of an elevation, lookingtoward the cyclone burners of the Fig. 1 unit;

Fig. 3 is an enlarged vertical section through one of the multiplelouver damper constructions for controlling and directing the flow oftempering gases into an upper part of the secondary furnace chamber;

Fig. 4 is a horizontal section of the Fig. 3 construction on the line 44of Fig. 3;

Fig. 5 is a detailed view of the tempering gas outlet indicated in Fig.3;

Fig. 6 is a diagrammatic view in the nature of a side sectional view ofa vapor generating and superheating unit of modified construction.

The main components of the Fig. 1 unit include cyclone burnerarrangements with upper and lower rows of cyclones A and B. They burncrushed coal, with the products of combustion discharging into a commonprimary furnace chamber 10 from which the combustion gases with thesmall remainder of the suspendedslag particles therein pass into thelower end of a vertically elongated secondary combustion chamber 12. Inthis combustion chamber gases contact the superheater including thedependent platens 14 and 16. The combustion gases pass through theoutlet 18 at the upper right hand part of the secondary combustionchamber to the the top of that wall. -.tubes continue as uprightcirculators 66 having end pordampered parallel heating gas :passes, toneof which preferablycontains one or-moreibanksof tubes forming :aconvection vapor reheater, with the other parallel passes having therein.banks of tubes constituting the primary vapor superheater including thetubes or banks aof tubes 118-123 inclusive.

The gases'fiowing through the lower part of the downflow gas pass, flowover the-elements of a bank 26 of economizer tubes into .ductwork orabreeching 28 leading to the inlet 30 of a tubular air heater 32.

In communication with the breeching 28 is the inlet 34 of the ductwork36 of a heating gas recirculation system which has one outlet formed bya tempering gas chamber 38 at the front wall 40 ofthe secondarycombustion chamber 12 and at .a position just above the primary furnacechamber 10. Another outlet for the recirculated gas system is formed bythe recirculating gas chamber 42 which is disposed below .the temperinggas chamber and in ,such position that'itis conveniently incommunicationwith the upper part ,ofthe primary furnace chamber 10.

Substantially, all if the vapor generation of the illustrative unittakes place in vapor generating wall tubes which are included in thewalls and other boundaries of the :cyciones, furnace chambers, andtheconvection gas :pass. In the natural circulation system of the unitthese -vapor generating tubes have their lower ends either di- .rectlyconnected to the liquid drum 44 at the bottom of the installation, orconnected to said drum through the intermediacy of appropriate headersand tubes. The upper ends of the vapor generating tubes are similarlyconnected to the liquid and vapor drum 46. Appropriate downcomers leadfrom the liquid space of the upper drum to the lower drum. .Suchdowncomers are formed bythe conduits 147 and associated tubularconnections.

Some of the vapor generating tubes lead to the left from the lower drum,with their initial portions 50 included in a fluid cooled slaggingbottom disposed between the slag pit 52 and the primary furnace chamber,portions of these tubes being bent aside over the slag pit to form anopening 54 through which slag flows to the pit. Beyond the floor 56 ofthe primary furnace chamber, these tubes continue in the left hand wall58 of that chamber and then around the outlets of the cyclones, one ofsaid outlets being indicated at 60. Thence, these tubes continueupwardly at '62 along the same wall of the primary combustion chamber,and thereafter, along the left hand wall of the secondary combustionchamber to At this position some of these tions 68 bent to the right fordirect communication with the liquid and vapor drum '46. Others of thesewall tubes continuealong the roof 70 of the secondary combustion chamberand then along the roof 72 of the convection gas pass 22 to a position74 near the rear wall 76 of that gas pass. From this point they are bentto extend to direct communication with the liquid and vapor drum, as at78.

The opposite or right hand wall 80 of the secondary combustion chamberincludes Wall tubes 82 extending directly from the upper part of thelower drum 44 with some of these tubes having their lower partsassociated with refractory material to form a part of the rear wall '80of the secondary furnace chamber. These wall tubes continue upwardly toform parts of a division wall 86 between the convection gas pass 22 andthe upper part of the secondary combustion chamber 12. Above the levelof the reheater and primary superheater 24, some of these wall tubes arebent out of their wall formation to provide a screen 88 across the gasinlet to the convection 'gas pass. These bent out tubes preferablycontinue along the roof 72 of the gas pass and thence are bent upwardlyto direct communication with the liquid and vapor drum 46. Others ofthese wall tubes continue through 'theroofof the unit, as at 90, tocommunication with the liquid and vapor drum 46.

The fluid cooled wall 92 which divides the primary and secondarycombustion chambers includes fluid cooled tubes leadingdirectly from thelower drum 44 and having lower parts which form the tubular slag screens94 and 96 extending across the flow of, gases from the primary furnacechamber to the secondary furnace chamber. Beyond these tubular screens,the tubes have portions forming the upright common wall extending toalevel just below the level of the header 98 which is disposed near thetop of the primary furnace chamber, and externally thereof. This headerhas riser connections (ineluding risers 100) with the drum 46. Alongopposite side walls of the secondary combustion chamber are upper andlower side wall headers 102 and 104 connected by upright vaporgenerating tubes 106. The headers 102 and 104 have appropriateconnections withthe drums 44 and 46.

The rear wall 76 of the convection gas pass'22 includes primarysuperheater inlet tubes 108 with their inlet ends connected to the upperheader 109 which in turn receives vapor from the vapor chamber of theliquid and vapor drum 46 through conduits 112. These Wall tubes .108discharge superheated vapor to the lower'header 114 at the right handlower corner of the convection gas pass. From other parts of thisheader, tubes 116 leading to the various return bend components of the"banks 118- -123- of primary superheater, extend. The outlet portions ofthese tubes, after forming the upper bank 123 of the primarysuperheater, extend along the rear wall of the inlet chamber, or gasmixing chamber 20 at the top of the convection gas pass, to an uppersuperheater header 126.

The cyclone furnaces A and B and other closely associated components areconstructed and arranged in a manner similar to that indicated in theUS. patent .to Bailey et al. 2,357,301, September 5, 1944, the walls ofthe cyclones including vapor generating tubes having their inlet endsleading directly from the lowermost header which is, in turn,appropriately connected to the lower drum 44. In conforming to thecylindrical or circular walls of the cyclones, the fluid cooling systemincludes appropriate lower and upper headers 132 and 134 for eachcyclone with connecting tubular elements 136 of substantiallysemi-circular formation. From the upper cyclone headers, risers 138 leaddirectly upwardly to junction with horizontal circulators 140 which havedirect communication with the liquid and vapor drum.

Supenheated vapor from the outlet header of the primary superheaterflows through conduits 142, 144 to the inlet header 146 at the upperleft hand part of the secondary superheater. This superheater isconstructed in accordance with the detailed description of the commonass'ignees co-pending application of J. E. Black, Serial No. 277,831filed March 21, 1952, now Patent No. 2,809,- 616, issued Oct. 15, 1957.It includes a number of U-bent tubes leading downwardly from the inletheader and then upwardly to form the first row 14 of the long platens.The lower parts of these platens below the lower ends of the interposedshort platens 148 have the adjacent tubes arranged in a closelycontiguous manner and in what may be termed a tu-be-to-tube relationshipto limit slag accumulation and enhance periodic slag removal. The upperparts of these long platens have their tubes somewhat spaced so thattheir width corresponds to the width of the shorter platens. From theoutlet ends of the tubes of the long platens of the first row, crossovertubes 150 extend to downfiow parts of the platens of the second row,these second row long platens being constructed in a manner similar tothat of the first row of long platens. The vapor flows downwardly to thelower ends of the long platens of the second row and then upwardlythrough the return bend legs of the U-tubes to an intermediate header152 at the upper right hand part of the secondary superheater, with theoutlet ends of the tubes of the longer platens connected incircumferential rows to this header. From -heater. inlet 34 of therecirculating gas system through the inlet flow in the secondary furnacechamber.

positions between these rows the tubes of the shorter platens 148 extenddownwardly to a position about half 'these upfiow portions, crossovertubes similar to those above referred to lead to the downflow tubes ofthe similarly constructed short platens of the remaining row. The outletends of the tubes of these platens are in alignment with the inlet tubesof the secondary superheater -to a position somewhat above the roof ofthe secondary combustion chamber. to the right to connections with theoutlet header 154 From that position they extend for the secondarysuperheater. This outlet header has a conduit 156 connected thereto forconducting the superheated steam to a point of use.

The longer superheater platens are arranged on 24" bridging across theseparts of the platens by accumula- -tions of slag particles which aredeposited thereon during the operation of the unit, the slaggingcharacteristics of this zone of the superheater being controlled by theintroduction of tempering gas into the secondary furnace chamber at aposition just below the secondary super- This tempering gas flows fromthe breeching ductwork 36 to the inlet of the fan 158 and thence throughother ductwork 160 to the zone which includes the tempering gas inletchamber 38 disposed adjacent the front wall 40 of the secondary furnacechamber 12. Fig.

' 2 shows this chamber as well as the chamber 42 as having and directedby multiple louver damper constructions,

each including a plurality of louvers or dampers 174-179 fixed topintles 180185 the outer ends of which have the crank arms 186 fixedthereto. The louvers 174179 of each construction are manually adjustableso that they may be fixed in closed position, open position, or at anyintermediate position directing the tempering gases in differentdirections at different angles transversely of gas The manually operableadjusting mechanism for these louvers includes parallel connections forthe louvers. These connections include the bar 190 which is pivotallyconnected to each of the crank arms 186. At its upper end this bar ispivoted to the crankarm 192 at 194, this crank arm being fixed to ashaft 196 geared to a countershaft 198 upon which a hand wheel 200 ismounted. The louvers for each of the outlets 164169 may be independentlyadjusted. In this way, the gases through one outlet may flow at anupwardly inclined direction across the secondary furnace chamber whilethe gases of the adjacent outlet flow obliquely downwardly across thegas flow of the secondary furnace chamber in order that adequate mixingof the gases may take place upon entry into the slagging Zone of thesecondary superheater.

The outlets for tempering gas are completed by fiat plate studs 202 and204 welded to the tubes 206 and 208, similar studs 210 and 212 welded tothe tubes 170 and 172, side wall members 216 and 214 welded to tubes 170and 172, and associated refractory 218.

As shown in Fig. 1, some of the rear wall tubes 82,

chamber preferably takes place over the upper part of 'the total loadrange of the unit with the flow of tempering gas increasing as the loadincreases, from a fractional load to full load, the flow of temperinggas being controlled by an automatic control system which may beinfluenced primarily from steam fiow, or load. Thus, the gastemperatures at positions below the lower parts of the short superheaterplatens are kept at such values that the solid particles ofincombustible residue of the fuel are generally not in a sticky orslagging condition beyond that point.

To maintain a predetermined superheat, recirculated gas is caused toenter the upper part of the primary furnace chamber from therecirculating gas inlet chamber 42 directly below the tempering gasinlet chamber, the walls of these chambers being formed by appropriateheat resisting material and insulating material. At the opposite inletends of the recirculating gas chamber 42 there are control dampers 162similar to those provided for the ends of the tempering gas chamber 38.These dampers may be automatically controlled from representations ofload, with or without modification by final steam temperature, andintermediate steam temperature at the attemperator. Recirculating gasflows from the inlet chamber 42 through openings provided in the lefthand wall of the primary furnace chamber. These openings are provided bythe bending of selected wall tubes out of their wall formation.

The Fig. 6 unit involves one or more cyclone burners 250 from which hightemperature furnace gases are discharged through the outlet 252 into theprimary furnace chamber 254. The furnace gases with the residualsuspended slag particles therein pass across tubular screens 256 and 258into the secondary furnace chamber 260.

The Fig. 6 embodiment has its superheater 262 formed by upright tubularsections connected for series flow and pendently supported across gasflow in the gas outlet 264 of the secondary furnace chamber 260. Thegases then proceed into the inlet 266 of the downflow gas pass 268wherein they first flow across the transverse tubes of the reheater 270and then across the banks of tubes constituting the primary superheater272, the inlet header 274 receiving steam through the conduit 276 fromthe steam and water drum 278.

Below the primary superheater 272 the gases pass across the transverselydisposed tubes of the economizer 280, thence into the breeching 282leading to the air heater.

Communicating with the breeching 282 between the economizer and the airheater is the inlet 284 of a recirculated gas system including inletductwork 286, the fan 288, and the outlet ductwork 290. This outletductwork leads to a recirculated gas chamber 292 from the upper part ofwhich controlled flow of the gases may pass through the tempering gasduct 294 into the upper part of the secondary furnace chamber 260. Fromthe lower part of the chamber 292, controlled flow of the returned gasmay be recirculated through the duct 296 through openings in the lefthand wall 298 of the secondary furnace chamber. These openings will beformed by bending some of the tubes of the wall 298 to the right towardthe secondary furnace chamber in spaced relation to the tubes of thewall 300 so as to form the recirculated gas duct or passage 302. Theposition of the tubes forming the right hand wall of this passage isindicated at 304 and 306 above the position at which these tubes fan outto form the screen 258. The associated screen 256 is similarly formed bythe fanning out of the tubes forming the right hand wall 300 of theprimary furnace chamber 254.

Tempering gas fiow through the duct .294'is controlled by a damper 310,and the control "of recirculated gas to the duct 296'to'the inlet of thesecondary furnace chamber is controlled by the damper 312. The vaporgenera- 'tion in the Fig. 6 unit takes place in the furnace wall tubes,and aside from the above described construction, the other pertinentfeatures of the Fig. 6 modification correspond with the structure of theFig. 1 unit.

In the operation of the'Fig. 6 unit sufiicient gas is recirculated atfull load, and introduced through duct 294 near the outlet of thesecondary furnace chamber to re- ,duce the gas temperatures to values ofthe order of 2000 F. at positions entering outlet 264. This may takeabout 20% recirculation. As the load drops, only suflicient gas 'isrecirculated through the duct 294 to hold the gas temperature enteringthe superheater down to values of the order of 2000 F. To maintain goodmixing, the entry of the tempering gas through the duct 294 may bedirected or controlled as described above with reference to the Fig. 1unit. This duct may be divided so that it has divisions leading to apartof the ductwork forming a tempering gas chamber similar to chamber 38 ofFig. 1, or a part ofthe duct extending across the furnace chamber :mayhave a series of vaned outlets similar to those described relative tochamber 38.

As the load drops, the amount of recirculated gas flow -'to-the primaryfurnace is increased to maintain desired vapor heating. Superheat iscontrolledby an interstage spray attemperator (not shown) functioningbetween the primary'superheater 272 and the secondary superheater "262.Only a small amount of attemperation isnecessary at full load, with theamount increasing as the load -drops. Therecirculation of gas throughthe duct 294 :near the "outlet of the secondary furnace chamber is forthe purpose of reducing the gas temperature entering the superheater.

While the 'Fig. '1 unit and the Fig. 6 unit are disclosed as involvingcyclone furnaces, it is to'be appreciated -that some features of theinvention maybe employed "with other types of fuel burners, the primaryrequisite of such other fuel burners being that they afford thepertinent high temperatures of the combustionproducts in orderthatthe'pertincnt high superheat may be attained.

'With the predominantly radiant superheater of the Fig. 'lunit, the gastempering feature of the invention is particularly effective as comparedto any similar installation employing a radiant superheater-of the walltube rtype,:and the gas tempering feature of the invention is alsoparticularly effective in the distribution of superheater andreheaterheat absorption (between the reheat- =er andthe secondarysuperheater) to maintain reheat at an optimum value at low loads whilesimultaneously 'minimizing draft loss which would otherwise be occa---sioned by increased damper control to effect increased gas flow overthe reheater-component of the convection gas pass. This effect existswhere dampers are employed to increase gasflow through a reheater gaspass with respect to parallel gas passes inwhichthe primary superiheaterisdisposed. A somewhat similar effect is pro- 'duced as to thedistribution of superheater absorbed heat :and reheater absorbed heat inthe pertinent type of installation which includes convectionreheatersurface'di'sposed in aconvection gas pass in advance of primarysuperheater surface in that gas pass. At a fractional load, if thetempering gas flow is increased, the radiant secondary'superheater heatabsorption decreases because of the ilowered gas temperatures and theconvection reheater'heat absorption increases because of the higher gasmass flow.

' Certain features of this invention are disclosed in my prior-copendingjoint application with A. E. Raynor, filed December -6, 1950, which hasissued as US. Patent No.

*While in accordance .with the provisions of the statutes "haveillustrated and described herein the best. forms of myinvention nowknown to me, those skilled in the cart will understand that the changesmaybe made in the forrnof the apparatus disclosed without departing fromthe spirit of the invention covered by my claims, and that certainfeatures of-my invention may sometimes be used to advantage without acorresponding use of other features.

I claim:

1. A vapor generating and superheating unit comprising verticallyextending walls defining a vertically elongated radiant chamber arrangedto receive heating gases at its lower end and having a heating gasoutlet at its upper end, vapor generating tubes lining a wall of saidradiant chamber, means defining a convection heating pass connected tosaid gas outlet, a bank of primary vapor superheating tubes in saidheating pass, a plurality of predominantly radiantly heated secondaryvapor superheating tube platens spaced across the upper part of saidradiant chamber, a furnace constructed to burn a slagforming fuel attemperatures above the fuel ash fusion temperature and arranged todischarge slag-carying heating gases through one of said walls into thelower end of said radiant chamber, means for withdrawing heating gasesfrom said convection heating pass downstream of said primarysuperheating tubes and mixing one portion of the withdrawn gases withthe heating gases as they discharge from said furnace, and means forintroducing another portion of the withdrawn gases into said radiantchamber at a level closely subjacent to the lower ends of said-vaporsuperheating tube platens.

2. A vapor generating and superheating unit comprising verticallyextending walls defining a vertically elongated radiant chamberarrangedto receive heating gases at its lower end and having a heatinggas outlet at its upper end, vapor. generating tubes lining a wall ofsaid radiant chamber, means defining a convection heating pass connectedto said gas outlet, a bank of primary vapor superheating tubes in saidheating pass, a plurality of predominantly radiantly heated secondaryvapor superheating tube platens spaced across the upper part of saidradiant chamber, a furnace constructed to burn a slagforming fuel attemperatures above the fuel ash fusion temperature and arranged todischarge slag-carrying heating gases through one of said walls, meansforming a verticallyextending baflle extending inwardly and downwardlyfrom said last named wall to a level adjacent the level of ,the heatinggases discharging from said furnace anddefining a primary furnacechamber therebetween opening to the lower end of said radiant chamber,means for withdrawing heating gases from said convection heating passdownstream of said primary superheating tubes and introducing oneportion of the withdrawn gases into said primary furnace chamber abovethe level of the heating gases discharging from said furnace, and meansfor introducing another portion of the withdrawn gases into said radiantchamber at a level closely subjacent to the lower ends of said vaporsuperheating tube platens.

3. A vapor generating and superheating unit comprising verticallyextending'walls defining a vertically elongated radiant chamber arrangedto receive heating gases at its lower end and having a heating gasoutlet at its upper end, vapor generating tubes lining a wall of saidradiant chamber, means defining a convection heating pass connected tosaid gas outlet, a bank of primary vapor superheating tubes in saidheating pass, a plurality of pendently supported secondary vaporsuperheating tube platens spaced across the upper part of said radiantchamber,a cyclone furnace constructed to burn a slag-forming fuel attemperatures above the fuel ash fusion temperature and arranged todischarge slag-carrying heating gases through one of said Walls, meansforming a vertically extending bafile extending inwardly and downwardlyfrom said last named wall to a level adjacent the level of the heatinggases discharging from said cyclone furnace and defining a primaryfurnace chamber therebetween opening to the lower end of said radiantchamber, meansfor withdrawing heating gases from said convection heatingpass downstream of said primary superheating tubes and introducing oneportion of the withdrawn gases into said primary furnace chamber abovethe level of the heating gases discharging from said cyclone furnace,means for introducing another portion of the withdrawn gases into saidradiant chamber at a level closely subjacent to the lower ends of saidpendent vapor superheating tube platens, and means for independentlyvarying the amount of withdrawn gases introduced at each location.

4. A vapor generating and superheating unit comprising verticallyextending walls defining a vertically elongated radiant chamber arrangedto receive heating gases at its lower end and having a heating gasoutlet at its upper end, vapor generating tubes lining a wall of saidradiant chamber, means defining a convection heating pass connected tosaid gas outlet, a bank of primary vapor superheating tubes in saidheating pass, a plurality of pendently supported secondary vaporsuperheating tube platens spaced across the upper part of said radiantchamber, a plurality of vertically spaced rows of cyclone furnacesconstructed to burn a slag-forming fuel at temperatures above the fuelash fusion temperature and arranged to discharge slag-carrying heatinggases through one of said walls, means including a row of vaporgenerating tubes forming a vertically extending baflle extendinginwardly and downwardly from said last named wall to a level adjacentthe level of the heating gases discharging from the lowermost row ofcyclone furnaces and defining a primary furnace chamber therebetweenopening to the lower end of said radiant chamber, means for withdrawingheating gases from said convection heatmg pass downstream of saidprimary superheating tubes and introducing one portion of the withdrawngases into said primary furnace chamber above the level of the heatinggases discharging from the uppermost row of cyclone furnaces, and meansfor introducing another portion of the withdrawn gases into said radiantchamber at a level closely subjacent to the lower ends of said pendentvapor superheating tube platens.

5. A vapor generating and superheating unit comprising verticallyextending walls defining a vertically elongated radiant chamber arrangedto receive heating gases at its lower end and having a heating gasoutlet at its upper end, vapor generating tubes lining a wall of saidradiant chamber, means defining a convection heating pass connected tosaid gas outlet, a bank of primary vapor superheating tubes in saidheating pass, a plurality of pendently supported secondary vaporsuperheating tube platens spaced across the upper part of said radiantchamber, a cyclone furnace constructed to burn a slag-forming fuel attemperatures above the fuel ash fusion temperature and arranged todischarge slag-carrying heating gases through one of said walls, meansincluding a row of vapor generating tubes forming a vertically extendingbaflle extending inwardly and downwardly from said last named wall to alevel adjacent the level of the heating gases discharging from saidcyclone furnace and defining a primary furnace chamber therebetweenopening to the lower end of said radiant chamber, means for withdrawingheating gases from said convection heating pass downstream of saidprimary superheating tubes and introducing one portion of the withdrawngases into said primary furnace chamber above the level of the heatinggases discharging from said cyclone furnace, means for introducinganother portion of the withdrawn gases in laterally spaced streams intosaid radiant chamber at a level closely subjacent to the lower ends ofsaid pendent vapor superheating tube platens, means for independentlyvarying the amount of withdrawn gases introduced at each location, andmeans for separately varying the angle of entry of said laterally spacedstreams relative to said wall.

6. A vapor generating and superheating unit comprising verticallyextending walls defining a vertically elongated radiant chamber arrangedto receive heating gases at its lower end and having a heating gasoutlet at its upper end, vapor generating tubes lining a wall of saidradiant chamber, means defining a convection heating pass connected tosaid gas outlet, a bank of convection heated vapor superheating tubes insaid heating pass, means for burning a slag-forming fuel at temperaturesabove the fuel ash fusion temperature and discharging slag-carryingheating gases through one of said walls, means including a row of vaporgenerating tubes forming a vertically extending fluid cooled bafileextending inwardly and downwardly from said last named wall to a leveladjacent the level of the heating gases discharging through said walland defining a primary furnace chamber therebetween opening at its lowerend to the lower end of said radiant chamber, and means for withdrawingheating gases from said convection heating pass downstream of said vaporsuperheating tubes and introducing the withdrawn gases into said primaryfurnace chamber at a location above the level of the heating gasesdischarging thereinto and at points distributed over a major portion ofthe width of said primary furnace chamber.

7. A vapor generating and superheating unit comprising verticallyextending walls defining a vertically elongated radiant chamber arrangedto receive heating gases at its lower end and having a heating gasoutlet at its upper end, vapor generating tubes lining a wall of saidradiant chamber, means defining a convection heating pass connected tosaid gas outlet, a bank of convection heated vapor superheating tubes insaid heating pass, a cyclone furnace constructed to burn a slag-formingfuel at temperatures above the fuel ash fusion temperature and arrangedto discharge slag-carrying heating gases through one of said walls,means including a row of vapor generating tubes forming a verticallyextending fluid cooled baflle extending inwardly and downwardly fromsaid last named wall to a level adjacent the level of the heating gasesdischarging from said cyclone furnace and defining a primary furnacechamber therebetween opening at its lower end to the lower end of saidradiant chamber, and means for withdrawing heating gases from saidconvection heating pass downstream of said vapor superheating tubes andintroducing the withdrawn gases into said primary furnace chamber at alocation above the level of the heating gases discharging thereinto fromsaid cyclone furnace and at points distributed over a major portion ofthe width 0 said primary furnace chamber.

8. A vapor generating and superheating unit comprising verticallyextending walls defining a vertically elongated radiant chamber arrangedto receive heating gases at its lower end and having a heating gasoutlet at its upper end, vapor generating tubes lining a wall of saidradiant chamber, means defining a convection heating pass connected tosaid gas outlet, a bank of convection heated vapor superheating tubes insaid heating pass, a cyclone furnace constructed to burn a slag-formingfuel at temperatures above the fuel ash fusion temperature and arrangedto discharge slag-carrying heating gases through one of said walls,baflie means including a row of vapor generating tubes and extendinginwardly and downwardly from said last named wall to a level adjacentthe level of the heating gases discharging from said cyclone furnace anddefining a recirculated gas chamber opening at its lower end to thelower end of said radiant chamber, means for withdrawing heating gasesfrom said convection heating pass downstream of said vapor superheatingtubes and introducing the withdrawn gases into said recirculated gaschamber at a location above the level of the heating gases dischargingfrom said cyclone furnace and at points distributed over a major portionof the width of said primary furnace chamber and downwardly along saidbaffle means, and means for varying the amount of withdrawn gases sointroduced.

9. A vapor generating and superheating unit comprising verticallyextending walls defining a vertically elongated radiant chamber arrangedto receive heating gases at its lower end and having a heating gasoutlet at its upper end, vapor generating tubes lining a wall of saidradiant chamber, means defining a convection heating pass connected tosaid gas outlet, a bank of convection heated vapor superheating tubes insaid heating pass, a plurality of vertically spaced rows of cyclonefurnaces constructed to burn a slag-forming fuel at temperatures abovethe fuel ash fusion temperature and arranged to discharge slag-carryingheating gases through one of said walls, means including a row of vaporgenerating tubes forming a vertically extending bafile extendinginwardly and down wardly from said last named wall to a level adjacentthe level of the heating gases discharging from the lowermost row ofsaid cyclone furnaces and defining a primary furnace chambertherebetween opening at its lower end to the lower end of said radiantchamber, and means for withdrawing heating gases from said convectionheating pass downstream of said vapor superheating tubes and introducingthe withdrawn gases into said primary furnace chamber at a locationabove the level of the heating gases discharging thereinto from theuppermost row of cyclone furnaces and at points distributed over a majorportion of the width of said primary furnace chamber.

10. A vapor generating and superheating unit comprising verticallyextending walls defining a vertically elongated radiant chamber arrangedto receive heating gases at its lower end and having a heating gasoutlet at its upper end, vapor generating tubes lining a wall of saidradiant chamber, means defining a convection heating pass connected tosaid gas outlet, a bank of primary vapor superheating tubes in saidheating pass, a plurality of pendently supported secondary vaporsuperheating tube platens laterally spaced across the upper part of saidradiant chamber, means for burning a slag-forming fuel at temperaturesabove the fuel ash fusion temperature and discharging slag-carryingheating gases through one of said walls into the lower end of saidradiant chamber, and means for withdrawing heating gases from saidconvection heating pass downstream of said primary superheating tubesand introducing the withdrawn gases into said radiant chamber at a levelclosely subjacent to the lower ends of said pendent vapor superheatingtube platens.

11. A vapor generating and superheating unit com prising verticallyextending walls defining a vertically elongated radiant chamber arrangedto receive heating gases at its lower end and having a heating gasoutlet at its upper end, vapor generating tubes lining a wall of saidradiant chamber, means defining a convection heating pass connected tosaid gas outlet, a bank of primary vapor superheating tubes in saidheating pass, a plurality of pendently supported secondary vaporsuperheating tube platens spaced across the upper part of said radiantchamber, means for burning a slag-forming fuel at temperatures above thefuel and ash fusion temperature and discharging slag-carrying heatinggases through one of said walls into the lower end of said radiantchamber, and means for withdrawing heating gases from said convectionheating pass downstream of said primary superheating tubes andintroducing the withdrawn gases into said radiant chamber at a levelclosely subjacent to the lower ends of said pendent vapor superheatingtube platens comprising a series of vertically elongated openings in oneof said radiant chamber walls, a series of multiple louver dampers ineach of said openings, and means for independently adjusting the seriesof dampers in said wall openings with respect to the vertical anglethereof relative to said wall.

12. A vapor generating and superheating unit comprising verticallyextending walls defining a vertically elongated radiant chamber arrangedto receive heating gases at its lower end and having a heating gasoutlet at its upper end, vapor generating tubes lining a wall or" s'aidradiant chamber, means defining a convection heating pass connected tosaid gas outlet, a bank of primary vapor superheating tubes in saidheating pass, a plurality of pendently supported secondary vaporsuperheating tube platens laterally spaced across the upper part of saidradiant chamber, a cyclone furnace constructed to burn a slag-formingfuel at temperatures above the fuel ash fusion temperature and arrangedto discharge slagcarrying heating gases through one of said walls intothe lower end of said radiant chamber, means for withdrawing heatinggases from said convection heating pass downstream of said primarysuperheating tubes and introducing the withdrawn gases in streamsthrough one of said vertical Walls into said radiant chamber at a levelclosely subjacent to the lower ends of said pendent vapor superheatingtube platens in intimate mixing relation With the heating gases flowingto said heating gas outlet, and means forming a gas-defiecting arch onthe vertical wall opposite said last named wall and arranged to deflectthe heating gases into mixing relation with said recirculated gasstreams.

13. A vapor generating and superheating unit comprising verticallyextending walls defining a vertically elongated radiant chamber arrangedto receive heating gases at its lower end and having a heating gasoutlet at its upper end, vapor generating tubes lining a wall of saidradiant chamber, means defining a convection heating pass connected tosaid gas outlet, a bank of primary vapor superheating tubes in saidheating pass, a plurality of pendently supported secondary vaporsuperheating tube platens spaced in parallel vertical planes across theupper part of said radiant chamber, alternate tube platens terminatingat their lower ends at substantially different levels in said radiantchamber, a cyclone furnace constructed to burn a slag-forming fuel attemperatures above the fuel ash fusion temperature and arranged todischarge slag-carrying heating gases through one of said walls into thelower end of said radiant chamber, means for withdrawing heating gasesfrom said convection heat* ing pass downstream of said primarysuperheating tubes and introducing the withdrawn gases into said radiantchamber at a level closely subjacent to the lower ends of the lowermostpendent vapor superheating tube platens, and means for varying theamount of withdrawn gases so introduced.

References Cited in the file of this patent UNITED STATES PATENTS1,828,483 Wood Oct. 20, 1931 1,964,149 Frisch June 26, 1934 2,100,190Jackson Nov. 23, 1937 2,109,840 Gordon Mar. 1, 1938 2,685,279 CaracristiAug. 3, 1954 2,730,080 Stallkamp Jan. 10, 1956 2,737,930 Rowand et a1Mar. 13, 1956 FOREIGN PATENTS 523,870 Great Britain July 24, 1940504,114 Great Britain Apr. 14, 1939 OTHER REFERENCES B & W BulletinG67-A of 1950 page 41.

